"billion" in the noun sense
1. billion, one million million, 1000000000000
the number that is represented as a one followed by 12 zeros in the United Kingdom the usage followed in the United States is frequently seen
2. million, billion, trillion, zillion, jillion, gazillion, bazillion
a very large indefinite number (usually hyperbole
"there were millions of flies"
3. billion, one thousand million, 1000000000
the number that is represented as a one followed by 9 zeros
"billion" in the adjective sense
denoting a quantity consisting of one thousand million items or units in the United States
denoting a quantity consisting of one million million items or units in Great Britain
Source: WordNet® (An amazing lexical database of English)
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